This invention relates to the safe operation of vessels that must be opened to the atmosphere as part of the operation. In one of its aspects this invention relates to the prevention of flow of operating materials into a vessel while the vessel is opened. In another of its aspects this invention relates to the prevention of opening of a vessel while the vessel is pressurized. More particularly, the invention relates to the safe operation of a pipeline pig launcher-receiver. In a narrow aspect the invention relates to a safety interlock system for a pipeline pig launcher-receiver having a dismountable closure.
The use of pipeline pigs is well known in the art. These devices which usually comprise two spaced-apart cup-shaped members suitably sized to provide sufficient blockage in a pipeline to allow them to be moved along the interior of the pipeline by fluid pressure are used as means for cleaning deposits from the inside of pipelines, as spacers between different types of flowing material to minimize contamination, and can be used to create a complete blockage of a pipeline for pressure testing purposes. Adequately to use these devices in fairly continuous service, pipelines are often equipped with pipeline pig launching or receiving stations as means for easily inserting the devices into a pipeline or removing them from the pipeline.
Since most pipelines operate with a relatively high fluid pressure in lines of thirty inch diameter or even more, a pig launching or receiving station can have a considerable fluid capacity, for instance, a thirty inch diameter pipeline can have a forty-two inch diameter station which usually will be of length considerably greater than the diameter of the pipe. While the inadvertent opening of such a receiver while it is full of fluid, particularly a liquid, could be a hazard to operating personnel and to the environment, the hazard both to personnel and the environment is greatly increased if there is a possibility of the inadvertent opening of a flow control valve allowing operating fluid to enter the vessel while the vessel is open to the atmosphere. I have developed an interlocking safety system which seeks to avoid the possibility of leakage from the pressured process lines into the vessel when the vessel is open and also seeks to prevent the opening of the system to atmosphere when the vessel is pressurized.
It is therefore an object of this invention to provide a safety interlock system for a vessel that can be opened to the atmosphere and that is separated from pressurized operating lines containing fluids by a system of valves. It is another object of this invention to provide a method and apparatus by which flow into a pipeline pig launcher-receiver can be prevented when this vessel is open to the atmosphere. It is another object of the invention to provide method and apparatus preventing the opening of a pipeline pig launcher-receiver while there is pressure within the vessel.
Other aspects, objects and the various advantages of this invention will become apparent to those reading this disclosure and the appended claims.